Qt4: Fix typo setting a variable for FindThreads.

Fixes bug 14055.

Modules/Qt4ConfigDependentSettings.cmake

@@ -260,7 +260,7 @@ if(Q_WS_X11)
   # X11 libraries Qt always depends on
   set(QT_QTGUI_LIB_DEPENDENCIES ${QT_QTGUI_LIB_DEPENDENCIES} ${X11_Xext_LIB} ${X11_X11_LIB})
 
-  set(CMAKE_THREAD_PREFER_PTHREADS 1)
+  set(CMAKE_THREAD_PREFER_PTHREAD 1)
   find_package(Threads)
   if(CMAKE_USE_PTHREADS_INIT)
     set(QT_QTCORE_LIB_DEPENDENCIES ${QT_QTCORE_LIB_DEPENDENCIES} ${CMAKE_THREAD_LIBS_INIT})